Conductive-polymer-coated electrode particles

ABSTRACT

An electro-active compound particulate coated with a conducting polymer composition finds use in electrochemical cell electrodes.

FIELD OF THE INVENTION

[0001] The present invention is concerned with electrode improvementswhich find use in solid or liquid electrochemical cells, and in general,wherever intercalation compounds have heretofore been used in compositeelectrodes with an electronically conducting material such as carbon.

BACKGROUND OF THE INVENTION

[0002] Solid secondary electrochemical cells consist of a solidelectrolyte interposed between an anode and a cathode. Preferably, thesolid electrolyte is a single-phase material consisting of a solidpolymeric matrix, an inorganic ion salt, and an electrolyte solvent.Preferably, the cathode is a composite material composed of anintercalation compound, carbon, solvents and a solid polymeric matrix.The anode may be composed of metals or of an intercalating material. Formany advantageous reasons, interest centers on lithium-basedelectrochemical cells and intercalating cathodes.

[0003] Solid electrochemical cells offer a number of advantages overelectrochemical cells containing a liquid electrolyte, includinglight-weight and high-energy density. Solid electrolytes are prepared inthin layers which reduce cell resistance and allow large drains atlow-current density. The solid electrolyte is usually composed of apolymeric matrix, a suitable salt and an electrolyte solvent which aidsconductivity and acts as a plasticizer for the polymer. Thepolymerization is normally carried out in a curing step performed on acomposition, including a polymer precursor, or prepolymer, whichundergoes radiation or heat-induced cross-linking reactions to form thepolymeric matrix. Suitable polymer precursors include, for example,poly(oxyalkylene) ethers, such as polyethylene oxide, andacryloyl-derivatized poly(oxyalkylene) ethers.

[0004] The solid electrolyte also contains a solvent chosen for lowervolatility and excellent capability with the other components of theelectrolyte as evidenced by conductivity, charge capacity and life-timeof the cell. Suitable solvents well-known in the art for use in solidelectrolytes including, by way of example, organic carbonates andglymes.

[0005] In a preferred method of manufacturing a solid electrochemicalcell, the solid electrolyte is cured on the surface of a cathode.Typically, the cathode is itself prepared by coating a mixture ofcathode-active material, the electroconductive such as carbon, a solidmatrix forming polymer precursor, and an electrolyte solvent on acurrent collector followed by curing with an electron beam. If the solidelectrolyte is then formed on this cathode surface, an anode materialcan then be laminated on to the solid electrolyte to form a solidelectrochemical cell.

[0006] It has been suggested that a conductive polymer may be used toreplace carbon as the conductive material in composite electrodes,particularly, composite cathodes. While the art recognizes that dopantsin one form or another are a necessary compliment to non-ionic organicmaterials in order to function as efficient conductors, and that a meansmust be found to efficiently incorporate the conducting polymer anddopant into the composite electrode, means of satisfactorilyaccomplishing this end have been lacking.

[0007] Many conducting polymers are difficult to work with and some aresimply intractable high molecular weight materials, insoluble inordinary solvents and prone to decomposition below their melting orsoftening point.

[0008] Co-pending U.S. patent application Ser. No. 08/163,209, filedDec. 6, 1993, the disclosure of which is incorporated herein in itsentirety, disclosed the replacement of carbon as the conductivecomponent of the cathode in an electrochemical cell. The goal ofreplacing carbon with conducting polymer was to improve theconductivity, in particular, the electronic conductivity of the cathodewith a lightweight substitute material.

[0009] It was suggested that compatible cathode-active materials, i.e.,intercalation compounds, be mixed with electronically conductingpolymer, and a binder, such as a polymeric binder, to form a positivecathode plate under pressure. Suitable cathode-active materials includedvanadium oxides, and suitable conductive polymers included polyaniline.

[0010] Electrodes made of a major amount of conducting polymer have beendeveloped for solid electrochemical cells, i.e., Fiona M. Gray, “SolidPolymer Electrolytes”, VCH Publishers, Inc., New York, 1991, pp. 5-9;U.S. Pat. Nos. 4,222,903; 4,519,939; 4,519,940; and 4,579,679, thedisclosures of each of which is incorporated herein in its entirety.

[0011] It would be advantageous if the method of making compositeelectrodes of cathode-active material and conducting polymers could beimproved. In particular, the art is searching for methods of handlingpolymeric conductors more efficiently to produce a more conductive, lessresistive, lower impedance cathode of high charge capacity andcyclability.

SUMMARY OF THE INVENTION

[0012] Electrodes finding use in solid electrochemical cells are made byforming an electrode paste composed of a solid matrix forming polymerprecursor, a compatible electrolyte solvent, and an electro-activematerial coated with a conducting polymer; coating the paste onto asubstrate; and curing the paste to a solid electrode. Preferably, theelectrode is a cathode and the cathode-active material is anintercalation compound.

[0013] The cathode-active material is a particulate which in anotheraspect of this invention, is coated by solubilizing a conductive polymercomposition with a solvent; mixing the solubilized conductive polymercomposition with particles of cathode-active material to form a mixture;and removing substantially all the solvent from the mixture to produce aparticulate product of cathode-active material coated with a conductingpolymer composition.

[0014] Another aspect of this invention is an electrode, preferably acathode, which contains particles of an electro-active material coatedwith a conducting polymer composition. Such a conducting polymercomposition may include any compatible conductive polymer, andpreferably a polymer composition selected from the group consisting ofpolyaniline, polyacetylene, polyquinoline, polyquinoxaline,poly(p-phenylene sulfite), poly(phenylquinoxaline), (poly(p-phenylene),polypyrrole, and polyphthalocyaninesiloxane. More preferably, theconducting polymer composition is composed of a major amount ofpolyaniline and a dopant.

[0015] In yet another aspect of the invention, the dopant is selected toprovide solubility to the polymer as well as to render the polymerconducting. Preferably, the conducting polymer composition is aprotonated polymer salt, for example, a protonated polyaniline salt,wherein the salt contains a counter-ion comprising a functional groupwhich assists solubility. Such conducting protonated polymer salts aresoluble in ordinary solvents such as pyrrolidine, tripropylene,tripropylamine, xylene, chloromethane, m-cresol, formic acid anddimethylsulfoxide.

[0016] In yet another aspect of the invention, the components of themanufacturing process consist of a mixture composed of a cathode-activematerial in particulate form, a solubilized conducting polymer and asolvent for the conducting polymer; and a cathode paste composed of asolid polymer matrix-forming polymer precursor, a particulate composedof cathode-active material particles coated with a conducting polymercomposition, and a compatible electrolyte solvent.

[0017] In yet another aspect of the invention, an electrochemical cellcontains an anode composed of compatible anodic materials, a cathodecomposed of compatible cathodic materials, and a solid electrolyteinterposed therebetween; wherein the solid electrolyte comprises a solidpolymer matrix, an inorganic ion salt, and an electrolyte solvent; andwherein the cathode comprises particles of a cathode-active materialcoated with a conducting polymer composition. A secondary batterycomprises at least two such cells.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 shows the charge capacity of an electrochemical cell of thepresent invention measured in milliampere hours, as the cell isdischarged, and the concurrent decrease in cell voltage.

[0019]FIG. 2 shows the change in the charge capacity of the cell withthe cell voltage, as the cell is discharged; comparing two cells, onecontaining a typical cathode, the other containing a cathode of thisinvention. Note that the voltage plateaus of FIG. 1 correspond to thedips in FIG. 2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS ON THE INVENTION

[0020] The invention is concerned with electrodes and their method ofmaking. Particularly of interest, are cathodes containing acathode-active particulate material coated with a conducting polymer,and solid electrochemical cells made therefrom.

[0021] However, prior to describing this invention in further detail,the following terms are defined below.

[0022] Definitions

[0023] As used herein, the following terms have the following meanings.

[0024] The term “solid polymeric matrix” refers to an electrolytecompatible material formed by polymerizing an inorganic or organicmonomer (or partial polymer thereof) and which, when used in combinationwith the other components of the electrolyte, renders the electrolytesolid. The solid matrix may or may not be ion conducting.

[0025] Suitable solid polymeric matrices are well known in the art andinclude solid matrices formed from inorganic polymers, organic polymersor a mixture of organic polymers with inorganic non-polymeric materials.Preferably, the solid polymeric matrix is an organic matrix derived froma solid matrix forming monomer and from partial polymers of a solidmatrix forming monomer.

[0026] Alternatively, the solid polymeric matrix can be used incombination with a non-polymeric inorganic matrix. See, for example,U.S. Pat. No. 4,990,413, which is incorporated herein by reference inits entirety. Suitable non-polymeric inorganic materials for use inconjunction with the solid polymeric matrix include, by way of example,β-alumina, silver oxide, lithium iodide, and the like. Suitableinorganic monomers are also disclosed in U.S. Pat. Nos. 4,247,499;4,388,385; 4,414,607; 4,394,280; 4,432,891; 4,539,276; and 4,557,985each of which is incorporated herein by reference.

[0027] The term “a solid matrix forming monomer” refers to inorganic ororganic materials which in monomeric form can be polymerized, preferablyin the presence of an inorganic ion salt, and a solvent mixture of anorganic carbonate and a glyme compound, to form solid matrices which aresuitable for use as solid electrolytes in electrolytic cells. Suitablesolid matrix forming monomers are well known in the art and theparticular monomer employed is not critical. Preferably, the solidmatrix forming monomers have at least one heteroatom capable of formingdonor acceptor bonds with inorganic cations (e.g., alkali ions). Whenpolymerized, such compounds form an ionically conductive matrix.

[0028] Examples of suitable organic solid matrix forming monomersinclude, by way of example, propylene oxide, ethyleneimine, ethyleneoxide, epichlorohydrin, acryloyl-derivatized polyalkylene oxides (asdisclosed in U.S. Pat. No. 4,908,283), vinyl sulfonate polyalkyleneoxides (as disclosed in U.S. patent application Ser. No. 07/918,438,filed Jul. 22, 1992, and entitled “SOLID ELECTROLYTES DERIVED BYPOLYMERIZATION OF VINYL SULFONATE POLYALKYLENE OXIDES” which applicationis incorporated herein by reference in its entirety), and the like aswell as mixtures thereof.

[0029] Examples of suitable inorganic solid matrix forming monomersinclude, by way of example, phosphazenes and siloxanes. Phosphazenemonomers and the resulting polyphosphazene solid matrix are disclosed byAbraham et al., Proc. Int. Power Sources Symp., 34th, pp. 81-83 (1990)and by Abraham et al., J. Electrochemical Society, Vol. 138, No. 4, pp.921-927 (1991).

[0030] The term “a partial polymer of a solid matrix forming monomer”refers to solid matrix forming monomers which have been partiallypolymerized to form reactive oligomers. Partial polymerization may beconducted for the purpose of enhancing the viscosity of the monomer,decreasing the volatility of the monomer, and the like. Partialpolymerization is generally permitted so long as the resulting partialpolymer can be further polymerized, preferably in the presence of asolvent, such as, a mixture of an organic carbonate and a glymecompound, to form solid polymeric matrices which are suitable for use assolid electrolytes in electrolytic cells.

[0031] The term “cured” or “cured product” refers to the treatment ofthe solid matrix forming monomer or partial polymer thereof underpolymerization conditions (including cross-inking) so as to form a solidpolymeric matrix. Suitable polymerization conditions are well known inthe art and include by way of example, heating the monomer, irradiatingthe monomer with UV light, electron beams, and the like. The resultingcured product preferably contains repeating units containing at leastone heteroatom such as oxygen or nitrogen which is capable of formingdonor acceptor bonds with inorganic cations (alkali ions). Examples ofsuitable cured products suitable for use in this invention are set forthin U.S. Pat. Nos. 4,830,939 and 4,990,413 which are incorporated hereinby reference in their entirety.

[0032] The solid matrix forming monomer or partial polymer can be curedor further cured prior to or after addition of the salt, solvent andviscosifier. For example, a composition comprising requisite amounts ofthe solid matrix forming monomer, salt, organic carbonate/glyme solventand viscosifier can be applied to a substrate and then cured.Alternatively, the solid matrix forming monomer can be first cured andthen dissolved in a suitable volatile solvent. Requisite amounts of thesalt, organic carbonate/glyme solvent and viscosifier can then be added.The mixture is then placed on a substrate and cured; removal of thevolatile solvent would result in the formation of a solid electrolyte.In either case, the resulting solid electrolyte would be a homogeneous,single phase product which is maintained upon curing, and does notreadily separate upon cooling to temperatures below room temperature.Accordingly, the solid electrolyte of this invention does not include aseparator as is typical of liquid electrolytes.

[0033] The term “salt” refers to any salt, for example, an inorganicsalt, which is suitable for use in a solid electrolyte. Representativeexamples of suitable inorganic ion salts are alkali metal salts of lessmobile anions of weak bases having a large anionic radius. Examples ofsuch anions are I⁻, B^(r−), SCN⁻, ClO₄, BF₄ ⁻, PF₆ ⁻, AsF₆ ⁻, CF₃COO⁻,CF₃SO₃ ⁻, and the like. Specific examples of suitable inorganic ionsalts include LiCIO₄, LiI, LiSCN, LiBF₄, LiAsF₆, LiCF₃SO₃, LiPF₆,(CF₃SO₂)₂NLi, (CF₃SO₂)₃CLi, NaI, NASCN, KI and the like. The inorganicion salt preferably contains at least one atom selected from the groupconsisting of Li, Na and K.

[0034] The term “organic carbonate” refers to hydrocarbyl carbonatecompounds of no more than about 12 carbon atoms and which do not containany hydroxyl groups. Preferably, the organic carbonate is a linearaliphatic carbonate and most preferably a cyclic aliphatic carbonate.

[0035] Suitable cyclic aliphatic carbonates for use in this inventioninclude 1,3-dioxolan-2-one (ethylene carbonate);4-methyl-1,3-dioxolan-2-one (propylene carbonate);4,5-dimethyl-1,3-dioxolan-2-one; 4-ethyl-1,3-dioxolan-2-one;4,4-dimethyl-1,3-dioxolan-2-one; 4-methyl-5-ethyl-1,3-dioxolan-2-one;4,5-diethyl- 1,3-dioxolan-2-one; 4,4-diethyl- 1 ,3-dioxolan-2-one;1,3-dioxan-2-one; 4,4-dimethyl-1,3-dioxan-2-one;5,5-dimethy-1-1,3-dioxan-2-one; 5-methyl-1,3-dioxan-2-one;4-methyl-1,3-dioxan-2-one; 5,5-diethyl- 1,3-dioxan-2-one; 4,6-dimethyl-1,3-dioxan-2-one; 4,4,6-trimethyl-1,3-dioxan-2-one; and spiro(1,3-oxa-2-cyclohexanone-5′,5′,1′,3′-oxa-2′-cyclohexanone).

[0036] Several of these cyclic aliphatic carbonates are commerciallyavailable such as propylene carbonate and ethylene carbonate.Alternatively, the cyclic aliphatic carbonates can be readily preparedby well known reactions. For example, reaction of phosgene with asuitable alkane-α,β-diol (dihydroxy alkanes having hydroxyl substituentson adjacent carbon atoms) or an alkane-α,γ-diol (dihydroxy alkaneshaving hydroxyl substituents on carbon atoms in a 1,3 relationship)yields an a cyclic aliphatic carbonate for use within the scope of thisinvention. See, for instance, U.S. Pat. No. 4,115,206, which isincorporated herein by reference in its entirety.

[0037] Likewise, the cyclic aliphatic carbonates useful for thisinvention may be prepared by transesterification of a suitablealkane-α,β-diol or an alkane-α,γ-diol with, e.g., diethyl carbonateunder transesterification conditions. See, for instance, U.S. Pat. Nos.4,384,115 and 4,423,205 which are incorporated herein by reference intheir entirety.

[0038] Additional suitable cyclic aliphatic carbonates are disclosed inU.S. Pat. No. 4,747,850 which is also incorporated herein by referencein its entirety.

[0039] The term “viscosifier” refers to a suitable viscosifier for solidelectrolytes. Viscosifiers include conventional viscosifiers such asthose known to one of ordinary skill in the art. Suitable viscosifiersinclude film forming agents well known in the art which include, by wayof example, polyethylene oxide, polypropylene oxide, copolymers thereof,and the like, having a number average molecular weight of at least about100,000, polyvinylpyrrolidone, carboxymethylcellulose, and the like.Viscosifiers are often components of the electrolyte and cathode.

[0040] The term “electrochemical cell” refers to a composite containingan anode, a cathode and an ion-conducting electrolyte interposedtherebetween.

[0041] The “anode” refers to an electrode for the half-cell reaction ofoxidation on discharge typically comprised of a compatible anodicmaterial. Such compatible anodic materials are well known in the art andinclude, by way of example, lithium, lithium alloys such as alloys oflithium with aluminum, mercury, tin, zinc, and the like, andintercalation based anodes such as carbon, tungsten oxides and the like.

[0042] The “cathode” refers to the counter-electrode to the anode and iscomprised of compatible cathodic materials, e.g., cathode-activeinsertion compounds. Such compatible cathodic materials are well knownin the art and include cathode-active material such as, by way ofexample, manganese oxides, molybdenum oxides, vanadium oxides, sulfidesof titanium, molybdenum and niobium, lithiated cobalt oxides, lithiatedmanganese oxides, lithiated nickel oxides, chromium oxides, copperoxides, and the like. The particular compatible cathodic materialemployed is not critical.

[0043] Among the cathode-active materials V₆O₁₃ is particularlypreferred, and other preferred materials include LiMnO₂, LiMn₂O₄,LiCoO₂, V₃O₈, LiNiO₂, Li₂Mn₂O₄, ω-V₂O₅ and ε-Cu_(0.2)V₂O₅.

[0044] The cathode-active material is used in the form of a particulatehaving a mean diameter of about 1-90 μm, preferably about 2-30 μm, andmore preferably about 4-15 μm.

[0045] The term “conducting polymer” refers to an organicpolymer-containing material which is capable of electronic conduction.The polymer is characterized by a conjugated network of double bonds.The virgin polymer is rendered conducting by interaction with a dopant(oxidation or reduction). The polymer is reacted with an electron donordopant or an electron acceptor dopant to modify its room temperatureconductivity. The electron donor or acceptor is known in the art asn-type and p-type dopants, respectively. Polyacetylene and polyanilineare examples of organic polymers whose room temperature electricalconductivity is modified over several orders of magnitude above itsinsulator state by the incorporation of dopants (U.S. Pat. No.4,222,093). Other examples of such polymers are polyquinoline,polyquinoxaline, poly(p-phenylene sulfite), poly(phenylquinoxaline),poly(p-phenylene), polypyrrole, and polyphthalocyaninesiloxane.

[0046] Electronically conducting polymers have a conductivity which hasbeen modified with electron acceptor or donor dopants to be greater thanthe conductivity of the virgin state of the polymer. The electro-activeorganic polymeric material is fabricated from a virgin polymer, bymodifying the polymer with electron donor dopants or electron acceptordopants. An n-type electro-active organic polymer is obtained byreacting the virgin polymer with reducing or electron donor dopants.Electron donor dopants induce n-type conductivity in the polymer bydonating electrons to the polymer and reducing the polymer to apolyanion and the dopant is oxidized to a charge neutralizing cation.Similarly, a p-type electro-active organic polymer is obtained byreacting the virgin polymer with oxidizing electron acceptor dopants.Electron acceptor dopants induce p-type conductivity in the polymer byoxidizing the polymer to a polycation and the dopant is reduced to acharge neutralizing anion.

[0047] Alternatively, the polymers can be oxidized or reduced to theirconductive form using electrochemical techniques. In this method, alsoknown as electrochemical doping, the polymer is immersed in a suitableelectrolyte solution and used as one electrode of an electrochemicalcell. Upon passing an electric current through the cell, the polymer isreduced or oxidized (depending upon the direction of current flow) andcharge compensating cationic or anionic dopants from the supportingelectrolyte are incorporated into the polymer. For both types of doping,the resulting electro-active polymer consists of a charged polymerbackbone incorporating charge compensating ionic dopants. The charges ofthe polymer and the charge compensating dopants balance so that theelectro-active polymer is electrically neutral. The oxidation orreduction proceeds by an electron transfer.

[0048] The desired value of the room temperature electrical conductivityof the dopant modified electro-active organic polymer can be adjusted bycontrolling the level of incorporation of the dopants into the virginpolymer. Alternatively, the desired value of the room temperatureelectrical conductivity of the dopant modified electro-active organicpolymer is preselected by controlling the length of the reaction timebetween the virgin polymer and dopants.

[0049] As heretofore described, the dopant counter ion in oxidation orreduction plays no further role other than to provide electricalneutrality. In a preferred embodiment of the present invention, thedopant counter ion assists in solubilizing the conducting polymer in areadily available solvent at room temperature and, in fact, the dopantcounter ion is selected to assist solubilization of the polymer inparticular solvents. In the following, the solubilization mechanism willbe described in terms of the solubilization of polyaniline by afunctionalized protonic acid, but it is evident that other solubilizingdopants may be used in reduction or oxidation (n-type or p-type doping).

[0050] High molecular weight polyaniline is an example of an intractablematerial. Melt processing is not possible because the materialdecomposes before softening. While polyaniline may be solution-processedfrom strong acids, it was generally accepted in the field of conductingpolymers that it is impossible to dope high molecular weight polyanilineto the conducting form in common non-polar or weakly polar organicsolvents until Y. Cao et al., Synthetic Metals, 48 (1992) 91-97,described the use of functionalized protonic acids to dope polyanilineand simultaneously render the resulting polyaniline salt soluble incommon organic solvents. The disclosure of the Cao et al. publication isincorporated herein by reference in its entirety.

[0051] Consider polyaniline which has been protonated by reaction with afunctionalized protonic acid, for example, in an aqueous medium withpH<2-3. If the virgin polymer is represented by P and the functionalizedprotonic acid is H⁺M⁻R, where H⁺is a proton, M⁺is an anion and R is asolubilizing group, then the reaction with the polymer produces HP⁺M⁻Rwhich is equivalent, for our purposes, to oxidation of the polymer.

[0052] The term “protonated polyaniline salt” refers to the conductingpolymer composition represented by HP⁺M⁻R.

[0053] The term “functionalized protonic acid” refers to an acid denotedH⁺M⁻R, where R is the functional group chosen to be compatible with anon-polar or weakly polar common organic solvent. An illustrativeexample is dodecylbenzenesulfonic acid (DBSA), wherein M⁻is SO₃ ⁻and Ris φC₁₂H₂₅. The long alkyl chain of DBSA leads to the solubilization ofpolyaniline in common solvents such as xylene, toluene, decalin, etc.

[0054] In general, M⁻is any compatible anion in a protonic acid and R isany organic solubilizing group, e.g., a hydrocarbyl or oxyhydrocarbylgroup of from about 3 to about 50 carbon atoms.

[0055] The term “polymer composition” refers to the doped polymer(oxidized, reduced or protonated).

[0056] The term “solubilized conducting polymer” refers to the definedconducting polymer composition in solution in a compatible solvent. Forexample, protonated polyaniline salt in xylene solution.

[0057] It is evident that the dopant counter ion in oxidation orreduction of any virgin conducting polymer may be functionalized tocontain a solubilizing group. In which event the solubilizing group maybe selected to assist solubilization of the polymer in a particularnon-polar or weakly polar common solvent, or any other solvent.

[0058] The terms “hydrocarbyl” and “oxyhydrocarbyl” refer to monovalentmoieties composed of hydrogen and carbon, and hydrogen, carbon andoxygen, respectively.

[0059] In the practice of the method of the present invention, it isnecessary to form a mixture comprising a cathode-active material inparticulate form, a solubilized conducting polymer, and a solvent forthe conducting polymer, as heretofore described, or the polymer may besolubilized by any method compatible with the objective of coating thecathode-active particles with conducting polymer. The cathode-activematerial, such as V₆O₁₃, is readily available in particulate form, ormay be ground in a grinding machine (Attritor Model S-1, Union Process,Akron, Ohio). The solvent is then substantially removed from the mixtureby any conventional means, preferably by spray drying. The need toremove the solvent emphasizes the preference for relatively volatilesolvents, preferably those having a boiling point less than about 200°C., more preferably less than 100° C.

[0060] The product remaining after substantially all the solvent isremoved from this mixture, is the cathode-active particulate coated withthe conducting polymer composition. Preferably, the particles areuniformally coated and preferably, they are coated with a layer ofconducting polymer composition of from about 0.1 μm to about 2 μm inaverage thickness. The product may be reground as heretofore describedto obtain a powder suitable for forming the cathode paste.

EXAMPLE

[0061] An electrochemical cell using V₆O₁₃ as the cathode-activematerial may be made in the foregoing manner from a conducting polymercomposition of polyaniline. This cell may be compared to a moreconventional electrochemical cell in which the cathode is made fromV₆O₁₃ mixed with carbon powder. Except for the use of coated V₆O₁₃particles instead of carbon powder, both cells are substantially asdescribed hereinafter and in U.S. patent application Ser. Nos.07/918,509, filed Jul. 22, 1992, and 08/049,212, filed Apr. 19, 1993,the disclosures of each of which is incorporated herein by reference inits entirety.

[0062] A cathode paste is prepared by combining the dry cathode-activeparticulate, coated with conducting polymer (e.g., V₆O₁₃ andpolyaniline, about 55 weight percent) with electrolyte solvents (e.g.,propylene carbonate and triglyme, 4:1, about 35 weight percent), and asolid polymeric matrix polymer precursor (e.g., polyethylene oxide,polyethylene olycol diacrylate and ethoxylated trimethylol-propanetriacrylate, 1:8.5:1.5, about 10 weight percent). All weight percentsare based on the total weight of the paste. This combination ofingredients is thoroughly mixed at moderate temperature (e.g., less thanabout 90° C.), to form the cathode paste.

[0063] The cathode paste noted above can be placed onto the adhesionlayer of a current collector by extrusion at a temperature of from about45° to about 48° C. A Mylar cover sheet can be placed over the paste andthe paste can be spread to a thickness of about 90 microns (μm) with aconventional plate and roller system and can be cured by continuouslypassing the sheet through an electron beam apparatus (Electro-curtain,Energy Science Inc., Woburn, Mass.) at a voltage of about 175 kV and acurrent of about 1.0 mA and at a rate of about 1 cm/sec. After curing,the Mylar sheet can be removed to provide for a solid cathode laminatedto an aluminum current collector.

[0064] 56 grams of propylene carbonate, 14 grams of triglyme, and 17grams of urethane acrylate (Photomer 6140, available from Harckos,Manchester, U.K.) can be combined at room temperature until homogeneous.The resulting solution can be passed through a column of 4A sodiatedmolecular sieves to remove water and then can be mixed at roomtemperature until homogeneous.

[0065] At this point, 3 grams of polyethylene oxide having a numberaverage molecular weight of about 600,000 available as Polyox WSR-205from Union Carbide Chemicals and Plastics, Danbury, Conn., can be addedto the solution and then dispersed while stirring with a magneticstirrer over a period of about 120 minutes. After dispersion, thesolution can be heated to between 60° C. and 65° C. with stirring untilthe viscosifying agent dissolves. The solution can be cooled to atemperature of between 45° and 48° C., a thermocouple can be placed atthe edge of the vortex created by the magnetic stirrer to monitorsolution temperature, and then 10 grams of LiPF₆ can be added to thesolution over a 120 minute period while thoroughly mixing to ensure asubstantially uniform temperature profile throughout the solution.Cooling can be applied as necessary to maintain the temperature of thesolution between 45° and 48° C.

[0066] In one embodiment, the polyethylene oxide can be added to thesolution via a mini-sieve such as a 25 mesh mini-sieve commerciallyavailable as Order No. 57333-965 from VWR Scientific, San Francisco,Calif.

[0067] The resulting solution should contain the following: ComponentAmount Weight Percent^(a) Propylene Carbonate 56 g 56 Triglyme 14 g 14Urethane Acrylate 17 g 17 LiPF₆ 10 g 10 PEO  3 g  3 Total 100 g  100 

[0068] Optionally, solutions which can be produced as above and whichcontain the prepolymer, the polyethylene oxide viscosifier, theelectrolyte solvent and the LiPF₆ salt can be filtered to remove anysolid particles or gels remaining in the solution. One suitable filterdevice is a sintered stainless steel screen having a pore size between 1and 50 μm at 100% efficiency.

[0069] Alternatively, the electrolyte solution can be prepared in thefollowing manner. Specifically, in this example, the mixing procedurecan be conducted using the following weight percent of components:Propylene Carbonate 52 weight percent Triglyme 13 weight percentUrethane Acrylate^(b) 20 weight percent LiPF₆ 10 weight percent PEO^(c) 5 weight percent

[0070] The mixing procedure employs the following steps:

[0071] 1. Check the moisture level of the urethane acrylate. If themoisture level is less than 100 ppm water, proceed to step 2. If not,then first dissolve the urethane acrylate at room temperature, <30° C.,in the propylene carbonate and triglyme and dry the solution oversodiated 4A molecular sieves (Grade 514, 8-12 Mesh from Schoofs Inc.,Moraga, Calif.) and then proceed to step 4.

[0072] 2. Dry the propylene carbonate and triglyme over sodiated 4 Åmolecular sieves (Grade 514, 8-12 Mesh from Schoofs Inc., Moraga,Calif.).

[0073] 3. At room temperature, <30° C., add the urethane acrylate to thesolvent prepared in step 2. Stir at 300 rpm until the resin iscompletely dissolved. The solution should be clear and colorless.

[0074] 4. Dry and then sift the polyethylene oxide through a 25 meshmini-sieve commercially available as Order No. 57333-965 from VWRScientific, San Francisco, Calif. While stirring at 300 rpm, add thedried and pre-sifted polyethylene oxide slowing to the solution. Thepolyethylene oxide should be sifted into the center of the vortex formedby the stirring means over a 30 minute period. Addition of thepolyethylene oxide should be dispersive and, during addition, thetemperature should be maintained at room temperature (<30° C.).

[0075] 5. After final addition of the polyethylene oxide, stir anadditional 30 minutes to ensure that the viscosifier is substantiallydispersed.

[0076] 6. Heat the mixture to 68° C. to 75° C. and stir until theviscosifier has melted and the solution has become transparent to lightyellow in color. Optionally, in this step, the mixture is heated to 65°C. to 68° C.

[0077] 7. Cool the solution produced in step 6 and when the temperatureof the solution reaches 40° C., add the LiPF₆ salt very slowly makingsure that the maximum temperature does not exceed 55° C.

[0078] 8. After the final addition of the LiPF₆ salt, stir for anadditional 30 minutes, degas, and let sit overnight and cool.

[0079] 9. Filter the solution through a sintered stainless steel screenhaving a pore size between 1 and 50 μm at 100% efficiency.

[0080] At all times, the temperature of the solution should be monitoredwith a thermocouple which should be placed in the vortex formed by themixer.

[0081] Afterwards, the electrolyte mixture is then coated by aconventional knife blade to a thickness of about 50 1m onto the surfaceof the cathode sheet prepared as above (on the side opposite that of thecurrent collector) but without the Mylar covering. The electrolyteshould be cured by continuously passing the sheet through an electronbeam apparatus (Electrocurtain, Energy Science Inc., Woburn, Mass.) at avoltage of about 175 kV and a current of about 1.0 mA and at a conveyorspeed setting of 50 which provides for a conveyor speed of about 1cm/sec. After curing, a composite can be recovered which contains asolid electrolyte laminated to a solid cathode.

[0082] The anode can comprise a sheet of lithium foil (about 51-76 μmthick) which is commercially available from FMC Corporation LithiumDivision, Bessemer City, N.C.

[0083] A sheet comprising a solid battery can be prepared by laminatingthe lithium foil anode to the surface of the electrolyte in the sheetproduced in step C above. Lamination can be accomplished by minimalpressure.

[0084] It was found that a conducting polymer cell made substantiallyas-described behaves as a secondary electrochemical cell capable of manycharge-discharge cycles with satisfactory charge capacity.

[0085]FIG. 1 plots a voltage of a polyaniline-containing cell of thepresent invention versus its capacity in milliampere hours in the courseof a typical discharge of the cell. It is noteworthy that the voltageplateau at 2.08 volts and the other voltage characteristics of theV₆O₁₃/polyaniline cell are at least as satisfactory as those of theV₆O₁₃/carbon cell. FIG. 2 offers a direct comparison of the differentialcell capacity versus voltage for the two types of cells. The dips inFIG. 2 correspond to the plateaus in FIG. 1 and demonstrate that theconducting polymer cell of the present invention not only mimics thegood performance of the carbon cell, but the slight shift in voltageshown in FIG. 2 is believed to be due to the lower resistivity in theconducting polymer cell, which is a highly satisfactory result.

[0086] While the invention has been described in terms of variouspreferred embodiments, the skilled artisan will appreciate the variousmodifications, substitutions, omissions and changes which may be madewithout departing from the spirit hereof. The descriptions of thesubject matter in this disclosure are illustrative of the invention andare not intended to be construed as limitations upon the scope of theinvention.

What is claimed is:
 1. A particulate material comprising acathode-active material coated with a conducting polymer composition. 2.The cathode comprising particles of a cathode-active material coatedwith a conducting polymer composition.
 3. A cathode according to claim 2wherein said conducting polymer composition comprises a major amount ofa polymer selected from the group consisting of: polyaniline,polyacetylene, polyquinoline, polyquinoxaline, poly(p-phenylenesulfite), poly)(phenylquinoxaline), poly(p-phenylene), polypyrrole, andpolyphthalocyaninesiloxane, and a minor amount of capable dopant.
 4. Acathode according to claim 2 wherein said conducting polymer compositioncomprises a major amount of polyaniline and a minor amount of acompatible dopant.
 5. A cathode according to claim 4 wherein saidconducting polymer composition comprises a protonated polyaniline salt.6. A particulate according to claim 1 wherein said cathode-activematerial is an intercalation compound.
 7. A particulate according toclaim 1 wherein said cathode-active material is a lithium intercalationcompound.
 8. A particulate according to claim 1 wherein saidcathode-active material is a chalcogenide.
 9. A particulate according toclaim 1 wherein said cathode-active material is an oxide of a metalselected from the group consisting of V, Mn, Co, Ni, Cr, Ti, Mo, and Nb.10. A particulate according to claim 1 wherein said cathode-activematerial is vanadium oxide.
 11. A particulate according to claim 1wherein said cathode-active material is V₆O₁₃.
 12. A particulateaccording to claim 1 wherein said cathode-active material is selectedfrom the group consisting of LiV₃O₈, V₆O₁₃, LiMn₂O₄, LiCoO₂, LiNiO₂,ω-V₂O₅ and ε-Cu_(0.2)V₂O₅.
 13. A mixture comprising: a cathode-activematerial in particulate form; a solubilized conducting polymer; and asolvent for said conducting polymer.
 14. A mixture according to claim 13whereif said solubilized conducting polymer comprises a protonatedpolyaniline salt and a solvent selected from the group consisting ofpyrrolidine, tripropylene, tripropylamine, xylene, chloromethane,m-cresol, formic acid and dimethylsulfoxide.
 15. A cathode pastecomprising: a solid matrix forming polymer precursor; a particulatecomprising cathode-active material particles coated with a conductingpolymer composition; and a compatible electrolyte solvent.
 16. A methodof making a product particulate comprising cathode-active materialparticles coated with a conducting polymer composition for use in solidcathodes comprises the steps of: solubilizing a conductive polymercomposition with a solvent; mixing said solubilized polymer compositionwith particles of cathode-active material to form a mixture; removingsubstantially all said solvent from said mixture to produce said productparticulate.
 17. A method of making a solid cathode comprising the stepsof: forming a cathode paste; coating the cathode paste onto a substrate;and curing said paste to a solid cathode; wherein said cathode pastecomprises: a solid matrix forming polymer precursor; a particulatecomprising a cathode-active material coated with a conducting polymer;and a compatible electrolyte solvent.
 18. A method according to claim 17wherein said electrolyte solvent is an aprotic solvent.
 19. A methodaccording to claim 17 wherein said electrolyte solvent is selected fromthe group consisting of glymes, organic carbonates, and mixturesthereof.
 20. A method according to claim 17 wherein said electrolytesolvent is selected from the group consisting of triglyme, propylenecarbonate and mixtures thereof.
 21. An electrochemical cell comprising;an anode composed of compatible anodic materials; a cathode composed ofcompatible cathodic materials; and a solid electrolyte interposedtherebetween; wherein said solid electrolyte comprises: a solid polymermatrix, an inorganic ion salt, and an electrolyte solvent; and whereinsaid cathode comprises particles of a cathode-active material coatedwith a conducting polymer composition.
 22. A battery comprising at leasttwo cells of claim 21 .